Tuesday, June 19, 2018

Valve CV


             Control valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "setpoint" to a "process variable" whose value is provided by sensors that monitor changes in such conditions.[1] Control Valve is also termed as the Final Control Element.
A control valve consists of three main parts in which each part exist in several types and designs:

Valve's actuator- The opening or closing of control valves is usually done automatically by electrical, hydraulic or pneumatic actuators.
Valve's positioner- Positioners are used to control the opening or closing of the actuator based on electric, or pneumatic signals. These control signals, traditionally based on 3-15psi (0.2-1.0bar), more common now are 4-20mA signals for industry, 0-10V for HVAC systems, and the introduction of "Smart" systems, HART, Fieldbus Foundation, and Profibus being the more common protocols.
Valve's body  - valve bodies are available to achieve specific flow regulation behavior of process fludes.


Globe Valve:  The name "globe" refers to the external shape of the valve, not the internal flow area.   A typical globe valve has a stem that is adjusted linearly (up and down) to change the position of the plug.  As the plug changes, the area for flow between the plug and seat (opening) changes.  Many different seat and plug designs are available to achieve desired relationships between the stem position and flow rate; see the discussion on valve characteristic below.  The standard plug must oppose the pressure drop across the valve, which is acceptable for small pressure drops.  For large pressure drops, a balanced globe valve is used to enable a valve with small force to open and close the plug.
 Ball:  The restriction for this body is a solid ball which has some part of the ball removed to provide an adjustable area for flow.  The ball is rotated to influence the amount of flow.  The example ball valve displayed through the link below has a tunnel through the ball, and the ball is rotated to adjust the fraction of the tunnel opening available for flow.  Other types of ball valves have different sections removed from the ball to give desired properties.
 Butterfly:  The butterfly valve provides a damper that is rotated to adjust the resistance to flow.   This valve provides a small pressure drop for gas flows.
 Diaphragm: The diaphragm valve has one surface which is deformed by the force from the valve stem to vary the resistance to flow.
 Gate:  These valves have a flat barrier that is adjusted to influence the area for flow.  These bodies are used primary for hand-operated valves and valves automated for emergency shutoff.
   Summary of  Control Valve Bodies
Valve Body
Advantages
Disadvantages
globe (unbalanced)
-large range
-good shutoff
-unbalanced forces
-high pressure loss
globe (balanced)
-high capacity
-large range
-balanced forces
-poor shutoff
-high pressure loss
ball
-high capacity
-tight shutoff
-moderate pressure drop applications
-tends to plug (except segmented ball)
butterfly
-high capacity
-low pressure loss
-slurry applications
-high torque
-large deadband
-affects flow through limited range (i.e.
0-60%)
-tight shutoff requires special seat material
diaphragm
-slurry applications
-corrosion resistant materials
-short diaphragm life
-limited pressure and temperature
-small range
gate
-tight shutoff
-used only with clean fluids


Thursday, June 2, 2016

Kuwait-Rigger/Millright Fitter/SS Erector/Fabricator ( Oil& Gas) interview on 7.6.2016 at Chennai

Kuwait-Rigger/Millright Fitter/SS Erector/Fabricator ( Oil& Gas)

 interview on 7.6.2016 at Chennai 


Dear Candidate, 

Kharif National in Kuwait, a leading Oil& Gas Company 

requires the following candidates with 5 years Indian 

experience in construction works in Oil & Gas for Kuwait. 

Rigger 

Millright Fitter 

Structural Steel Fabricators/Erectors 

The salary is Rs.23000 to 27000/-. 

approximately. 

Free food and accommodation. 

Interview at Chennai on 7.6.2016 at our Associate 

office. 

Pl register your name with Ms.Kalaiarasi at 

9043224415/ Mr.Lakshmanan at 9677119752. 

Bring CV,Passport,Photo,Experience and education 

certificate.Interview venue will be intimated later. 

Regards, 

Kalaiarasi, 

Green HR Services, 

5,23 rd St,Jai Nagar, 

Chennai-106.

Saturday, January 16, 2016

Vibration Measurement Basics


 Measured Characteristics:

Amplitude
Frequency
Phase Angle
Absolute Phase Angle

Relative Phase Angle


AMPLITUDE
Peak-to-peak refers to the total amount of vibration.
Zero-to-peak refers to the total amount of vibration from the
maximum height of either the positive or negative peak to the
zero voltage axis.
Root mean square (RMS) is a function of the signal conditioning performed in the                                                                                      monitor or diagnostic instrument and not                                                                              the output of the transducer.


Frequency
Frequency is defined as the repetition rate of a periodic vibration within a unit of time.
The frequency of vibration (cycles per minute) is most often expressed in multiples of rotative speed of the machine.
Basic frequency measurements can be performed with an oscilloscope and Keyphasor signal.

PHASE
Phase is defined as the timing relationship, in degrees between two or more signals.









          .The phase angle is defined as     the number of degrees from the   Keyphasor pulse to the first positive peak of vibration.










Measurement References

The three basic frames of reference for vibration measurements on rotating machines are:
Rotor motion relative to the bearing (Shaft relative Vibration).
Casing motion relative to a fixed reference (Casing Absolute Vibration).
Rotor motion relative to a fixed reference (Shaft Absolute Vibration).



Position  of  Measurements
lAxial Position
wThrust Position
wRotor Position
lRadial Position
lDifferential Expansion
lCase Expansion
lEccentricity

Axial Position



Thrust Position





















lMeasurement of the position of the thrust collar in the thrust bearing assembly and how much bearing material may be used up.


Rotor Position 






Radial Position: 




















    Proximity Probes are used in The X-Y configuration to measure
radial vibration, the dc signal from  the transducer can be used to
indicate the radial position   of the rotor within the bearing



Differential Expansion








Case Expansion






                                  Eccentricity











How does Vibration Start?

Energy must be put into the system through an applied force, either internal or external. 

The force may be instantaneous, an impulse, or continuous.  In machines this energy is diverted from the process.  This reduces the machine’s efficiency and may also result in damage to the machine’s components.